The present invention relates to an electrical temperature sensor with a resistance film pattern as a measurement resistor provided with electrical terminals on an electrically insulating surface of a substrate, in particular made of ceramic, wherein the resistance film pattern is covered with a diffusion blocking film.
From International Patent Application Publication No. WO 92/15101 a fast platinum metal temperature sensor is known, having a platinum resistance film applied on a ceramic substrate and a passivation layer is applied over this resistance film, wherein the passivation layer is formed as a double film made of a ceramic film and a glass film.
For production of such a temperature-dependent resistor as a temperature sensor, the resistance film (Pt meander) is applied as a thick film on a substrate having a surface made of electrically insulating material, wherein the outer surface of the resistance film is covered by a layer made of electrically insulating material, which is used as a passivation layer.
Furthermore, from European Patent Application Publication No. EP 0 543 413 A1 a method is known for producing a resistor, having temperature-dependent platinum as a temperature sensor, wherein an electrode is applied at a spacing to the resistance film. Here, if ion migration caused by current conduction to the resistance film is to be avoided, the electrode is connected in an electrically conductive manner to the resistance film.
From U.S. Pat. No. 5,202,665 a method is known for the production of a temperature sensor, wherein a platinum film is applied on a substrate using thick-film technology. Here, platinum powder is mixed with oxides and bonding agents and is applied using screen printing. Then, a heat treatment in the temperature range between 1300° C. and 1350° C. is performed. A temperature sensor produced in this way with a film having platinum on a substrate contains finely divided metallic platinum in an oxide ceramic and has a metallic platinum content in the range of 60 to 90 wt. %.
From European Patent EP 0 327 535 B1 a temperature sensor is known having a thin-film platinum resistor as a measurement element. A temperature measurement resistor made of platinum is formed on a surface of an electrically insulating substrate, wherein the resistor element is covered with a dielectric protective film, which is preferably made of silicon dioxide and which has a thickness in the range of 2000-4000 Ängstrom. Furthermore, as a cover layer, a diffusion blocking film is provided, which is applied by precipitation of titanium in an oxygen atmosphere for forming titanium oxide. This blocking film has a thickness in the range of 6,000 to 12,000 Ängstrom. Also, if the diffusion blocking film allows the oxygen to access the dielectric film and thus essentially prevents an attack of metal ions coming free from the glass film on the platinum film, this can still, nevertheless, under extreme environmental conditions lead to an attack on the platinum film, so that its physical behavior as a temperature measurement element is disrupted.
Furthermore, an electrical measurement resistor for a resistance thermometer as well as a method for producing such an electrical measurement resistor are known from U.S. Pat. No. 4,050,052 and the counterpart German Patent DE 25 27 739 C3.
According to European Patent Application Publication No. EP 0 973 020, such temperature sensors can be equipped with a sacrificial cathode and can withstand temperatures up to 1100° C. This technology protects the measurement resistor against chemical or mechanical attacks. For this sensor, however, it must always be taken care that the cathode is connected correctly electrically, because a mix-up of the electrical connections leads to destruction of the sensor. Incidentally, at temperatures above 700° C. the sensor is subject to drift.